In particular, and without losing a general character, the present description refers to an apparatus for coating an electric conductor by means of an extrusion process, with a sheath having at least two layers or stripes of different or differently coloured materials.
Apparatuses of this kind contain at least two extruders for plastic materials, each of them being connected to a respective supply duct for each respective plastic material. Moreover, at least two plastic material exhaust ducts are provided, which can be selectively connected to the aforesaid supply ducts by means of a distributing device.
In traditional systems, plastic materials in a fluid/rubbery state pass only through the half of the number of supply ducts, namely an extruder is assigned to each series of channels, whereas the other half of the ducts is in a non operative state, namely they are extruders connected to the extrusion head but not in use.
This originates a relevant technical problem, namely that in non active ducts, therefore in auxiliary extruders which are not in use, some plastic material remains which in time hardens and/or deteriorates, thus obstructing or polluting the plastic material moving from the main extruder.
Therefore, the machine must be frequently stopped to clean the obstructed ducts and to replace the closure or distribution ring of the head any time a layer of plastic material must be removed and/or added, or if the auxiliary extruder must be excluded. This obviously involves a remarkable loss of time and of finished product.